You used to be a lawyer in New York. How did you come to be a burger flipper in London?

I was working in corporate law, which meant laborious hours and very monotonous work, and my college roommate's mother had opened up a burger place. I went to visit, and I asked if I could work at brunch on Sundays and be the bartender for a couple of hours a week, just to break up my day job.

I had a serious moment when I tried the burgers; it was like nothing I had ever tasted before. I was 28 at the time. I'm American, so I've been eating burgers all my life, but this burger, no joke, changed my life. I haven't had any burger come close to it since.

Bleecker Burger founder Zan Kaufman

Bleecker Burger founder Zan Kaufman

So I pretty much quit my law job the next week – it's not as brave as it sounds because I already knew I was moving to London to get married the next year – and then the next year I worked at this restaurant, learning as much as I could about the process. The most valuable lesson I took from the woman who ran it – a powerful matriarchal figure – was her relentless commitment to every aspect of the food. Nothing was ever good enough, and if it wasn't to her standards we didn't serve it. I saw that in action for a year and it really penetrated my psyche, and that has never left me.

Did that restaurant influence the burgers that would eventually be served at Bleecker?

The burgers are pretty different, the only thing that I definitely took from them was the mixed fries – part-sweet potato, part-normal – but the burgers are built differently. Theirs came on nice plates, they had different sizes, and they had Kobe and non-Kobe, so the building blocks of the burgers are very different, but the fundamentals of how you made them were the same. And she had really good relationships with their suppliers.

How have you seen London's street food scene change since you arrived?

I was so lucky, because when I started Bleecker I rode a magical wave of street food. I came in as the storm was taking off and we got carried through that, which was very fortunate. They say timing is everything, and it really was for Bleecker.

The street food scene then was so alive and rogue and infectious, and it was so nice to be part of that community, with the traders, with KERB, with Street Feast. I moved to London and all of a sudden I had 40 friends, and we were all in this together. I still think of that community as my community in London, and we were in it with the customers at the time, which I think is probably the difference with street food now. The customers from that time, a lot of them are my friends now.

Do you think street food in London is no longer the realm of outsiders?

I wouldn't say it's mainstream yet – I still think there's a lot of people who won't eat from those sort of environments.

I imagine that there's probably a sense of community, but I don't know if it's to the same extent. You are still in it together, it's hard, it's a grind, and you can commiserate and celebrate together. But it's probably much more transient now, and it probably seems more approachable. There are more markets, where more people are trying to get in, and maybe they don't realise how hard it is to make it as a business. So maybe the lifespan of street food traders is shorter.

It's hard. It's really hard. And I think if I had to do it again right now from the beginning I'm not sure I could get there, because it takes every ounce of energy you have to get through it. And at the beginning you're doing everything – you're doing the marketing, you're doing the admin, you're doing the food, you're doing the hiring – and it's so physical as well. You need that fresh set of eyes and excitement about it. That's why I always thought restaurateurs transitioning into street food seemed a bit wrong. They didn't have that real spark and that integrity. The motivations are different, and I can smell it from a block away. But it's inevitable: people see opportunities and they're going to try to pounce on them.

Tell us about the new restaurant

It's going to be in the most beautiful setting I've ever seen in a corporate building; Bloomberg have not spared any expense. So for Bleecker to be inside somewhere like that, compared to a car park in Dalston, where we started, is a bit of a juxtaposition.

There are more seats than we've ever had before; we can potentially fit up to 50 people in a very small site – we're talking 500 square feet – so it's still small and intimate and buzzy, but people can sit down. We'll probably have more different kinds of beer and wine on tap, but our key food items will still be our key food items. I can't imagine playing around with the menu that much.

Your street food truck and stall is quite different from your newer restaurants. Does there come a point where you have to put that worry about being 'cool' to one side?

Yes. For me, when we were just the truck, my favourite place to trade ever was the Gherkin. My background is in New York, where it's about speed – it's lunch and it's exciting. So now we're going back to the City in Bloomberg I feel like I'm finally getting the spot that I always wanted to have. When I thought about having a burger place it started in my mind as a shop, and I wanted it to be in the City. So now we've come full circle. If you talk about 'cool' customers, to me the customers at the Gherkin are the coolest: they're the nicest, and they're so interested in the food. To me, that's cool.

If I had to do it again, I'm not sure I could get there

It's a really difficult thing that I try not to be conscious about, because I think anytime you start to lead with 'cool' it's disastrous. I never want to do something because it's cool; I want to do something because I like it and it feels right. But as we grow, it's inevitable that this question is going to come up a bit more.

I try to keep it at bay because really what drives me is commitment to the burger. That's always been my driving force. I've been learning to be a leader, and at every stage of our growth the leadership is very different, but what I think I've learned is that you can't focus on too many things, because if you have too many things that you're trying to get across you get nothing across.

Have you got plans beyond this restaurant? Is there an endgame?

I definitely think a lot more about that now. I've never thought about an endgame or my exit strategy, though, because how can I exit from something that I love so much?

I can't imagine going past ten restaurants. Whether those are in other cities? I'd love to go to Paris; eventually it would be very nice to go back to New York – even though it would be very daunting, that for me would be the cherry on the top. But I'm not willing to do it unless I can keep the product at its level, which is going to be the biggest challenge.